Many portable electronic devices employ one or more batteries to provide a source of electrical power. Where such devices also employ semiconductor components such as a microprocessor or memory chip, it is often desirable for the device to include a DC-DC converter to convert the battery voltage, e.g. typically 6 or 9 volts, to a level, e.g. between 1 volt and 4 volts, suitable for application to the semiconductor components. It is desirable, in order to maximise the useful life (service time) of the batteries between charges, to provide a DC-DC converter which is as efficient as possible.
Similarly, other forms of DC-DC converter provide voltage changes between an input voltage and an output voltage, e.g. a step up in voltage or a change from a voltage in a range of given input voltages to a particular desired output voltage. In these various forms of converter it is always desirable to maintain good efficiency.
DC-DC converters employ electronic switch circuits. In particular, many converters employ a switch known as a synchronous rectifier, which is typically a voltage driven semiconductor device, which serves as a controllable device in place of a rectifier diode. A known control circuit for a synchronous rectifier includes a zero crossing detector to prevent unwanted reverse current flow in the synchronous rectifier.
It has been found that operation of the zero crossing detector in known electronic switches circuits which operate as synchronous rectifier circuits is not ideal. Undesirably, this has a deleterious effect on the converter efficiency.